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In vitro method to differentiate isolates of type III Streptococcus agalactiae from symptomatic and asymptomatic
1Department of Microbiology, University of Texas Health Science Center, San Antonio 78284.
Abstract:
Streptococcus agalactiae (group B streptococci) isolates from infected infants have been demonstrated to have three- to fourfold or higher levels of cell-associated lipoteichoic acid than isolates from asymptomatically colonized infants, suggesting a role for this cell surface polymer in the relative virulence of these organisms. The present study indicates that symptomatic isolates of type III group B streptococci can be readily differentiated from asymptomatic strains by their response to various levels of phosphate in a chemically defined medium (FMC). Both classes of isolates had the same doubling time (TD of 30 to 35 min) in FMC containing 65 mM sodium phosphate. However, levels of phosphate greater than 125 mM distinguished the two classes of strains. Asymptomatic strains pregrown in 65 mM phosphate to the stationary phase rapidly initiated growth at elevated phosphate levels, while symptomatic strains initiated growth only after a prolonged incubation period (greater than 400 min). These results suggest that the physiological growth response of clinical isolates of group B streptococci to phosphate can serve as a diagnostic aid in screening potentially virulent strains in pregnant women and newborn infants.
Insights
Group B Streptococcus (GBS) strains causing infant infections show higher lipoteichoic acid. Phosphate levels differentiate virulent GBS, aiding early detection in pregnant women and newborns.
Area of Science:
- Microbiology
- Infectious Diseases
- Biochemistry
Background:
- Streptococcus agalactiae (group B Streptococcus) isolates from infected infants exhibit higher cell-associated lipoteichoic acid levels compared to asymptomatic strains.
- Lipoteichoic acid is a cell surface polymer implicated in the virulence of group B Streptococcus.
Purpose of the Study:
- To investigate the differential physiological responses of symptomatic and asymptomatic group B Streptococcus strains to varying phosphate concentrations.
- To determine if phosphate response can serve as a diagnostic marker for potentially virulent group B Streptococcus strains.
Main Methods:
- Culturing of symptomatic and asymptomatic type III group B Streptococcus strains in a chemically defined medium (FMC) with varying sodium phosphate concentrations.
- Measuring doubling times and growth initiation after exposure to elevated phosphate levels (greater than 125 mM).
Main Results:
- Both symptomatic and asymptomatic strains exhibited similar doubling times (30-35 min) in FMC with 65 mM sodium phosphate.
- Asymptomatic strains initiated rapid growth at elevated phosphate levels (>125 mM) after pre-growth in 65 mM phosphate.
- Symptomatic strains showed a prolonged lag phase (greater than 400 min) before initiating growth at elevated phosphate levels.
Conclusions:
- The differential growth response of group B Streptococcus strains to phosphate levels can distinguish between symptomatic and asymptomatic isolates.
- This physiological characteristic offers a potential diagnostic aid for screening potentially virulent group B Streptococcus strains in pregnant women and neonates.
- Understanding these differences can contribute to improved strategies for preventing and managing group B Streptococcus infections.